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rfc:rfc6729

Internet Engineering Task Force (IETF) D. Crocker Request for Comments: 6729 Brandenburg InternetWorking Category: Standards Track M. Kucherawy ISSN: 2070-1721 Cloudmark, Inc.

                                                        September 2012
          Indicating Email Handling States in Trace Fields

Abstract

 This document registers a trace field clause for use in indicating
 transitions between handling queues or processing states, including
 enacting inter- and intra-host message transitions.  This might
 include message quarantining, mailing list moderation, timed
 delivery, queuing for further analysis, content conversion, or other
 similar causes, as well as optionally identifying normal handling
 queues.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6729.

Copyright Notice

 Copyright (c) 2012 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Crocker & Kucherawy Standards Track [Page 1] RFC 6729 Email Handling States September 2012

Table of Contents

 1. Introduction ....................................................2
 2. Key Words .......................................................3
 3. Trace Clause ....................................................3
 4. Discussion ......................................................6
 5. Granularity .....................................................6
 6. IANA Considerations .............................................7
    6.1. MAIL Parameters Additional-registered-clauses
         Sub-Registry ...............................................7
    6.2. MAIL Parameters Registered-states Sub-Registry .............7
 7. Security Considerations .........................................9
 8. References .....................................................10
    8.1. Normative References ......................................10
    8.2. Informative References ....................................10
 Appendix A.  Trace Field Examples .................................11
   A.1.  Typical Delivery without Obvious Extra Handling ...........11
   A.2.  Delivery with Moderation ..................................11
 Appendix B.  Acknowledgements .....................................12

1. Introduction

 [SMTP] defines the content of email message trace fields, commonly
 the "Received" header field.  These are typically used to record an
 audit trail of the path a message follows from origin to destination,
 with one such field added each time a message moves from one host to
 the next.
 Section 3.7.2 of that document mentions that "the most important use
 of Received: lines is for debugging mail faults [...]".
 There are some cases where there may be large time gaps between trace
 fields.  Though this might be caused by transient communication
 issues, they might also be caused by policy decisions or special
 processing regarding the content of the message, authorization of
 some identity on the message, or transitions between major software
 components.  Common examples include message quarantines (filters
 that cause a message to be held pending further evaluation or
 delivery of a message pending manual operator action), pending
 content analysis, or mailing list servers that impose moderation
 rules (mailing list owner action required regarding mail from authors
 not subscribed to those lists).

Crocker & Kucherawy Standards Track [Page 2] RFC 6729 Email Handling States September 2012

 This document registers a new optional clause that can be used in
 trace fields to indicate that a message entered such a special
 processing queue or state for some period.  This allows inspection of
 the trace information to reveal that the cause for a time gap in
 trace fields was imposed by additional processing rather than one
 caused by transient technical difficulties.

2. Key Words

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [KEYWORDS].

3. Trace Clause

 This specification defines a clause, called "state", which MAY be
 used when creating a Received header field (see Section 4.4 of
 [SMTP]) to indicate the nature of additional handling imposed on the
 relaying of a message toward its recipient(s).  It is followed by a
 single keyword that provides that detail.  A Mail Transfer Agent
 (MTA) or other handling agent that determines a message has entered a
 state other than normal queuing of messages for relaying or delivery
 MAY generate a trace field including one of these clauses.  That is,
 the presence of this clause on a trace field is an indication of the
 entry of the message into that state; a later trace field added would
 indicate its departure from that state.
 An MTA implementing this specification SHOULD add a Received field as
 described whenever:
 a.  It determines that a special handling condition will occur and
     places it into that condition; or
 b.  It determines that no special handling is required and prepares
     it for relay to the next handling agent.
 An MTA need not add a Received field indicating preparation for
 normal handoff to the next handling agent if it has already added a
 Received field for some other reason.  Trace data added by the next
 handling agent will imply the message's exit from the special
 handling condition.
 If a single MTA processes a message through multiple special handling
 conditions, it MAY add a Received field for each distinct condition.

Crocker & Kucherawy Standards Track [Page 3] RFC 6729 Email Handling States September 2012

 For example, presume a message will be injected into MTA-1, then
 travel to MTA-3 via MTA-2, and then MTA-3 will enact final delivery.
 At MTA-2, it is determined that some action will be taken that will
 cause the message to undergo some handling change that is outside of
 typical message flow.  In this case:
 1.  MTA-1 adds a typical Received field and relays it to MTA-2.
 2.  MTA-2 determines that the atypical handling will occur and adds a
     Received field using the extension specified here.
 3.  On completion of the atypical handling, MTA-2 relays the message
     to MTA-3.
 4.  MTA-3 adds a typical Received field and enacts final delivery of
     the message.
 Appropriate use of this mechanism does not include associating meta-
 data with the message, such as categorizing the message (e.g., the
 notions of "is spam" or "was 8-bit, converted to 7-bit").  Processing
 agents also cannot reliably use this mechanism to determine anything
 about the message content, since there is no guarantee that all
 agents in the chain of handling made such annotations to allow
 correct conclusions.  The sole purpose here is to allow one to
 determine the point(s) in the chain of custody of a message at which
 the message was subjected to handling outside of normal message
 routing and queuing.
 The following state keywords are defined in this document; extensions
 may define other registered keywords (see Section 6.2):
 auth:  The message entered a queue pending authentication of some
    identifier in the message.
 content:  The message entered a queue pending content analysis, such
    as scanning for spam or viruses.
 convert:  The message entered a queue pending content conversion.
 moderation:  The message entered a hold pending mailing list
    moderator action.
 normal:  The message is not in an administrative hold and is queued
    for or is being handed off to the next handling agent (which may
    be local delivery).  This is the default interpretation when no
    "state" clause is present.

Crocker & Kucherawy Standards Track [Page 4] RFC 6729 Email Handling States September 2012

 other:  The message entered a hold or queue for reasons not covered
    by other keywords in this list and not for transient technology
    issues.
 outbound:  The message entered a queue for outbound relaying.  This
    is typically the last case added for a single host, and the next
    Received header field is expected to be added by some other host.
 quarantine:  The message entered a hold in an isolation queue pending
    operator action for local policy reasons.
 timed:  The message entered a hold in order to meet a requested
    delivery window, such as is defined in [FUTURERELEASE].
 In Section 6, the "state" clause is added to the Additional-
 Registered-Clauses IANA sub-registry.  The ABNF for this clause is:
    State = CFWS "state" FWS queue-state-keyword [ "/" value ]
    queue-state-keyword = ( reg-state-keyword / unreg-state-keyword )
    reg-state-keyword = ( "auth" / "content" / "convert" /
                          "moderation" / "normal" / "other" /
                          "outbound" / "quarantine" / "timed" /
                          additional-state-keyword )
    additional-state-keyword = token
                             ; MUST be registered; see
                             ; "IANA Considerations" below
    value = token
    unreg-state-keyword = token
 "FWS" and "CFWS" are defined in [MAIL]. "token" is defined in [MIME].
 A transfer agent making use of this extension MAY also include header
 field comments to provide additional information.
 The "value" is available for providing additional labels as
 explanation for the state transition.  Examples could include:
 o  convert/unicode2ascii
 o  moderation/not-subscribed
 o  quarantine/spam

Crocker & Kucherawy Standards Track [Page 5] RFC 6729 Email Handling States September 2012

4. Discussion

 Handling agents are not expected to implement or support all of
 these.  Indeed, recording trace information for all of the states
 described above could make the header of a message inordinately
 large.  Rather, an agent is encouraged to apply state annotations
 when a message enters a handling queue where a significant condition
 occurs or where significant additional processing or delay is
 possible, and especially when a handoff has occurred between two
 different, independent agents.
 For example, an MTA receiving a message, doing message
 authentication, scanning for viruses and spam, and then putting it in
 an outbound queue could add four Received header fields denoting each
 of these states.  However, where they are all done as part of a
 single system process, in a single pass, doing so would be considered
 unusual (and extremely verbose).  This method SHOULD NOT be applied
 except when doing detailed analysis of a single component to identify
 performance issues with those steps.
 Rather, an agent that wishes to make a state annotation SHOULD add
 only a single Received header field including such annotation, thus
 indicating (a) the time of completion of its handling of the message
 via the date portion of the field and (b) the final disposition of
 that message relative to that agent.  For example, an MTA receiving a
 message that performs various checks on the message before
 immediately handing it off to a Mailing List Manager (MLM) would only
 record a "normal" state, assuming it passes those checks.  The MLM
 would then evaluate the message and record its own state once it
 decides what the next step will be for the handling of that message.

5. Granularity

 The degree of granularity -- and therefore the degree of verbosity --
 recorded through the use of this additional trace clause is likely to
 vary depending on circumstances.  It will typically be the case that
 use of this clause will be limited to "unusual" transitions, such as
 when a message requires additional scrutiny or other processing or
 needs to be quarantined.
 Somewhat greater granularity might also include transitions of
 administrative responsibility, such as between a Mail Transfer Agent
 (MTA) operator and a Mailing List Manager (MLM) operator.  This could
 be further enhanced to note some transitions that are interesting
 only when other transitions have occurred, such as noting entry to
 the outbound queue only when the message is originating from an
 "interesting" source, like an MLM, since an MLM can introduce
 significant changes to the message or delivery delay and it could be

Crocker & Kucherawy Standards Track [Page 6] RFC 6729 Email Handling States September 2012

 useful to know when it completed its processing, as distinct from the
 subsequent processing by the originating MTA.  In circumstances
 needing very fine-grained trace information, fields might be created
 to note all of these "significant" network architecture transitions.
 One should note, however, when choosing higher levels of granularity,
 that the Received header fields present on a message could be counted
 by MTAs when trying to decide whether or not a message routing loop
 is in effect.  A message with an abundance of these might cause an
 incorrect determination that the message is in a delivery loop,
 causing it to be removed from the mail stream.  See Section 6.3 of
 [SMTP] for further discussion.

6. IANA Considerations

6.1. MAIL Parameters Additional-registered-clauses Sub-Registry

 This document adds the following entry to the "Additional-registered-
 clauses" sub-registry of the "MAIL Parameters" registry, created by
 [SMTP]:
 Clause name:  state
 Description:  Indicates entry into a special queue state
 Syntax Summary:  state <state-name>
 Reference:  [RFC6729]

6.2. MAIL Parameters Registered-states Sub-Registry

 The "MAIL Parameters" registry at IANA has been updated by the
 creation of the "Registered-states" sub-registry to contain valid
 state keywords for use with this specification.  Updates to this
 registry are governed by the First Come, First Served rules of [IANA]
 for new registrations.  Changes to the status of existing entries are
 limited to the original registrant or IESG approval.
 Discussion of all registry updates is encouraged via one or more IETF
 mailing lists that typically cover email-related subjects prior to
 approval of the change, as a way of documenting the work.  The
 ietf-smtp@ietf.org list is suggested.
 Note that only registrations of queue state keywords are permitted.
 The registry is not to be used for specifying secondary information
 (i.e., the "value" part of the ABNF in Section 3).

Crocker & Kucherawy Standards Track [Page 7] RFC 6729 Email Handling States September 2012

 Registrations are to include the following entries:
 Name:  The name of the state keyword being defined or updated, which
    conforms to the ABNF shown in Section 3.
 Description:  A brief description of the keyword's meaning.
 Specification:  The specification document that defines the queue
    state being registered, or if no stable reference exists, a more
    detailed explanation of the queue state than is in the
    "Description", sufficient to allow interoperability.
 Use:  One of "current" (the state keyword is in current use),
    "deprecated" (the state keyword is in use but not recommended for
    new implementations), or "historic" (the state keyword is no
    longer in substantial current use).

Crocker & Kucherawy Standards Track [Page 8] RFC 6729 Email Handling States September 2012

 The initial registration set is as follows:
  +------------+------------------------+-----------------+---------+
  | Name       | Description            | Specification   | Use     |
  +------------+------------------------+-----------------+---------+
  | auth       | Held for message       |    [RFC6729]    | current |
  |            | authentication         |                 |         |
  +------------+------------------------+-----------------+---------+
  | content    | Held for message       |    [RFC6729]    | current |
  |            | content analysis       |                 |         |
  +------------+------------------------+-----------------+---------+
  | convert    | Held for message       |    [RFC6729]    | current |
  |            | content conversion     |                 |         |
  +------------+------------------------+-----------------+---------+
  | moderation | Held for list          |    [RFC6729]    | current |
  |            | moderation             |                 |         |
  +------------+------------------------+-----------------+---------+
  | normal     | Message is not being   |    [RFC6729]    | current |
  |            | held other than to     |                 |         |
  |            | accommodate typical    |                 |         |
  |            | relaying handling      |                 |         |
  +------------+------------------------+-----------------+---------+
  | other      | Held for causes not    |    [RFC6729]    | current |
  |            | covered by other       |                 |         |
  |            | registered state       |                 |         |
  |            | keywords               |                 |         |
  +------------+------------------------+-----------------+---------+
  | outbound   | Message placed in      |    [RFC6729]    | current |
  |            | outbound queue         |                 |         |
  +------------+------------------------+-----------------+---------+
  | quarantine | Held for operator      |    [RFC6729]    | current |
  |            | action due to content  |                 |         |
  |            | analysis or local      |                 |         |
  |            | policy                 |                 |         |
  +------------+------------------------+-----------------+---------+
  | timed      | Held to accommodate a  |    [RFC6729]    | current |
  |            | specific requested     |                 |         |
  |            | delivery window        |                 |         |
  +------------+------------------------+-----------------+---------+

7. Security Considerations

 The use of this trace information can reveal hints as to local policy
 that was in effect at the time of message handling.
 Further discussion about trace field security can be found in Section
 7.6 of [SMTP].

Crocker & Kucherawy Standards Track [Page 9] RFC 6729 Email Handling States September 2012

8. References

8.1. Normative References

 [IANA]           Narten, T. and H. Alvestrand, "Guidelines for
                  Writing an IANA Considerations Section in RFCs",
                  BCP 26, RFC 5226, May 2008.
 [KEYWORDS]       Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.
 [MAIL]           Resnick, P., Ed., "Internet Message Format",
                  RFC 5322, October 2008.
 [MIME]           Freed, N. and N. Borenstein, "Multipurpose Internet
                  Mail Extensions (MIME) Part One: Format of Internet
                  Message Bodies", RFC 2045, November 1996.
 [SMTP]           Klensin, J., "Simple Mail Transfer Protocol",
                  RFC 5321, October 2008.

8.2. Informative References

 [FUTURERELEASE]  White, G. and G. Vaudreuil, "SMTP Submission Service
                  Extension for Future Message Release", RFC 4865,
                  May 2007.

Crocker & Kucherawy Standards Track [Page 10] RFC 6729 Email Handling States September 2012

Appendix A. Trace Field Examples

 This section includes a sample of the new trace field clause in use.

A.1. Typical Delivery without Obvious Extra Handling

 Typical message delivery
      Received: from newyork.example.com
                (newyork.example.com [192.0.2.250])
            by mail-router.example.net (8.11.6/8.11.6)
                with ESMTP id i7PK0sH7021929
                for <recipient@example.net>;
            Fri, Feb 15 2002 17:19:22 -0800
      Received: from internal.example.com
                (internal.example.com [192.168.0.1])
            by newyork.example.com (8.11.6/8.11.6)
                with ESMTP id i9MKZCRd064134
                for <recipient@example.net>;
            Fri, Feb 15 2002 17:19:08 -0800
 Example 1: Typical message delivery with no appreciable extra
 handling; only Received header fields shown

A.2. Delivery with Moderation

 Message delivery after moderation
      Received: from newyork.example.com
                (newyork.example.com [192.0.2.250])
            by mail-router.example.net (8.11.6/8.11.6)
                with ESMTP id i7PK0sH7021929
                for <recipient@example.net>;
            Fri, Feb 15 2002 18:33:29 -0800
      Received: from internal.example.com
                (internal.example.com [192.168.0.1])
            by newyork.example.com (8.11.6/8.11.6)
                with ESMTP id i9MKZCRd064134
                for <secret-list@example.com>
                state moderation (sender not subscribed);
            Fri, Feb 15 2002 17:19:08 -0800
 Example 2: Message held for moderation; only Received header fields
 shown
 The message passed from internal.example.com to newyork.example.com
 intended for a mailing list hosted at the latter.  For list
 administrative reasons, the message is held there for moderation.  It

Crocker & Kucherawy Standards Track [Page 11] RFC 6729 Email Handling States September 2012

 is finally released over an hour later and passed to the next host.
 A comment after the state expression indicates the actual cause for
 the administrative hold.

Appendix B. Acknowledgements

 The authors wish to acknowledge the following for their reviews and
 constructive criticisms of this proposal: Tony Finch, Ned Freed, Carl
 S. Gutenkunst, John Levine, Bill McQuillan, S. Moonesamy, Alexey
 Melnikov, Robert A. Rosenberg, Hector Santos, Rolf Sonneveld, and
 Mykyta Yevstifeyev.

Authors' Addresses

 D. Crocker
 Brandenburg InternetWorking
 675 Spruce Dr.
 Sunnyvale  94086
 USA
 Phone: +1.408.246.8253
 EMail: dcrocker@bbiw.net
 URI:   http://bbiw.net
 Murray S. Kucherawy
 Cloudmark, Inc.
 128 King St., 2nd Floor
 San Francisco, CA  94107
 USA
 EMail: superuser@gmail.com

Crocker & Kucherawy Standards Track [Page 12]

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